Optical or opto-electronic device having a trapping layer in contact with a semiconductive layer

Abstract

Apparatus according to the invention comprises an optical, or opto-electronic device that comprises one or more "trapping" layers that can speed the decay of a non-equilibrium carrier distribution in an active region of the device, thereby improving device characterstics. In preferred embodiments the trapping layers are arranged so as to increase the likelihood of radiative recombination of carriers leading to erased heat sinking requirements.

What is claimed is: 
     
       1. Apparatus comprising (a) a source of electromagnetic radiation of wavelength λ o  ;   (b) at least one optical or opto-electronic device comprising a quantity of a first semiconductor material, during at least part of the time of operation of the apparatus the device is exposed to radiation from the source of radiation, and a non-equilibrium density of electrons and/or holes is caused to be present in the first semiconductor material during at least part of the time of operation of the apparatus; and   (c) means that are responsive to the density of electrons and/or holes in the first semiconductor material;   characterized in that   (d) the device further comprises at least one layer (to be referred to as the "trapping layer") of a second material in contact with the first semiconductor material, the second material chosen such that at least one of the electrons and/or holes has a lower potential energy in the second material than in the first semiconductor material, whereby at least some of the electrons and/or holes that enter the trapping layer from the first semiconductor material are being trapped in the trapping layer such that the non-equilibrium density of electrons and/or holes in the first semiconductor material can be decreased.   
     
     
       2. Apparatus of claim 1, where exposure of the device to the radiation results in a spatially non-uniform intensity of radiation in the device, and the at least one trapping layer is located in a region of relatively low intensity of the radiation. 
     
     
       3. Apparatus of claim 1, wherein the second material is a second semiconductor material, associated with the first and second semiconductor materials being a first and second bandgap energy, respectively, with the second bandgap energy being at least kT less than the first, where k is the Boltzmann constant and T is the absolute temperature of the first semiconductor material. 
     
     
       4. Apparatus of claim 1, wherein the second material is a metal. 
     
     
       5. Apparatus of claim 3, wherein the first semiconductor material is selected from the group consisting of GaAs and InGaAsP, and the second semiconductor material is selected from the group consisting of III-V semiconductors, the II-VI semiconductors, heavily doped Si and heavily doped Ge. 
     
     
       6. Apparatus of claim 1, wherein the quantity of the first semiconductor material comprises a multiple quantum well structure consisting of alternating layers of a relatively high and relatively low bandgap semiconductor material. 
     
     
       7. Apparatus of claim 2, wherein the second material is a second semiconductor material, and wherein associated with the second semiconductor material is a peak luminescence wavelength λ e  >λ o , and wherein the device parameters are selected such that luminescence of the second semiconductor material results in a relatively high intensity of the radiation of wavelength λ e  in at least a part of the device, with the at least one trapping layer being located in the region of relatively high intensity of radiation of wavelength λ e , whereby radiative recombination of electrons and holes in the second trapping layer is enhanced and non-radiative recombination is decreased. 
     
     
       8. Apparatus of claim 2, wherein the device is a Fabry-Perot etalon, associated with the etalon being a series of tranmission peaks and a standing wave pattern comprising at least one nodal plane, with the at least one trapping layer being located at or close to the nodal plane and having a thickness substantially less than λ o  /2n, where n is the refractive index of the first semiconductor material at λ o . 
     
     
       9. Apparatus of claim 8 comprising a multiplicity of trapping layers, wherein the standing wave pattern comprises a multiplicity of nodal planes, with each trapping layer located at or close to a nodal plane, wherein the second material is a second semiconductor material, associated with the second semiconductor material is a peak luminescence wavelength λ e  >λ o , and wherein the device parameters are selected such that λ o  at least approximately coincides with a first transmission peak of the etalon and λ e  at least approximately coincides with a second transmission peak of the etalon, and such that at least one of the trapping layers is located in a region of relatively high intensity of radiation of wavelength λ e , whereby radiative recombination of electrons and holes in the trapping layer is enhanced and non-radiative recombination is decreased. 
     
     
       10. Apparatus of claim 9, wherein the device can lase with the wavelength of the emitted laser radiation being substantially equal to λ e . 
     
     
       11. Apparatus of claim 2, wherein associated with the device is a longitudinal direction, and the trapping layer is essentially perpendicular to the longitudinal direction. 
     
     
       12. Apparatus of claim 2, wherein the device has at least one side surface, with the trapping layer being essentially parallel to the side surface and being located at or close to the side surface. 
     
     
       13. Apparatus of claim 12, wherein the side surface is formed by a relatively high bandgap material that is in contact with the trapping layer, whereby non-radiative recombination of electrons and holes in the trapping layer is decreased. 
     
     
       14. Apparatus of claim 6, wherein the trapping layer is located within a layer of the relatively low bandgap semiconductor material (a "well"), and wherein the second material is either a metal or is a semiconductor whose bandgap is lower than the bandgap of the relatively low bandgap semiconductor material that forms the well. 
     
     
       15. Apparatus of claim 6, wherein the trapping layer is located within a layer of the relatively high bandgap semiconductor material and close to a layer of the relatively low bandgap semiconductor material (a "well"), such that electrons and/or holes can tunnel from the well into the barrier layer. 
     
     
       16. Apparatus of claim 1, further comprising means for injecting electrons and/or holes into the first semiconductor material. 
     
     
       17. Apparatus of claim 16, wherein the means for injecting comprise a p-n junction. 
     
     
       18. Apparatus of claim 1, wherein the trapping layer is a metal layer, and further comprising means for making electrical contact with the trapping layer. 
     
     
       19. Apparatus of claim 1, wherein the device is a Fabry-Perot etalon comprising two mirrors and wherein the trapping layer is a metal layer, with the trapping layer being a mirror of the etalon. 
     
     
       20. Apparatus of claim 1, further comprising means for applying an electric field to the device whereby the movement of electrons and/or holes from the first semiconductor material into the trapping layer can be enhanced. 
     
     
       21. Apparatus of claim 1, wherein the first semiconductor material is compositionally graded such that the movement of electrons and/or holes from the first semiconductor material into the trapping layer is enhanced. 
     
     
       22. Apparauts of claim 1, wherein the apparatus is an optical computer, an optical data processing apparatus or an optical communication apparatus. 
     
     
       23. Apparatus of claim 21, comprising a multiplicity of optically isolated Fabry-Perot etalons.